Japanese Patent Application Publication No. 2013-195805 discloses a process cartridge in which a developing unit is movable relative to the drum unit. In such a conventional process cartridge, micromotion of the developing roller in accordance with surface irregularities of the photosensitive drum can be realized during developing operation, since the developing unit is movable relative to the drum unit. Further, during monochromatic printing, a developing roller for the color of black cam bring into contact with a corresponding photosensitive drum, while remaining developing rollers for other colors can be spaced away from corresponding photosensitive drums.
Further, according to such conventional technique, the developing unit includes a developing electrode for applying developing bias to the developing roller. An electrode provided at a housing of a printer is biased by a spring to contact the developing electrode. Thus, electric power can be supplied from the printer housing to the developing rollers through respective electrodes.